With the introduction of high efficiency infrared reflective coated halogen lamps, the filament size has become more compact and, therefore, more susceptible to shock. Hot shock is a failure mode known to lamp makers where two or more primary or secondary turns of an incandescent filament touch, adhere to one another, and short out a portion of the active filament, resulting in an early burnout of the filament. Over the years, data has been collected from actual customer applications that indicate hot shock damage in this type of lamp occurs during the initial installation with the power on. As customers with hundreds of lamps complained of early hot shock failures, new lamps of the same design were installed with the power off, and the hot shock failures were greatly reduced. In a very few cases, the problem persisted due to vibration caused by construction in the area.
Presently, the primary solution to the hot shock problem requires that the filament be designed with increased spacing between turns of the filament and/or the addition of higher levels of nitrogen. In either case, the lamp efficacy is reduced, and in many cases, the only solution is to install the lamps with the power turned off.